1. Field of the Invention
The present invention generally relates to devices used for the hypodermic injection of medication into or the withdrawal of fluid from a human patient and, more particularly, with a hypodermic syringe which employs a post-injection protective sheath about the needle tip.
2. Prior Art
The prior art discloses many devices for injecting medication into or withdrawing body fluids from human patients. Typically, devices taught by the prior art include syringes which receive measured quantities of medication to be injected or which can be used to draw samples of the patient's blood. Because these devices utilize injection needles, they are generally of a disposable nature and therefore discarded after a single use. Because of the risk of contamination, it is critical that individuals be protected from inadvertent contact with the needle tip after the hypodermic syringe has been used. This is particularly important when the needles have been applied to patients capable of contaminating the needles with blood-transmitted diseases such as hepatitis or acquired immune deficiency syndrome.
U.S. Pat. No. 4,804,371 is representative of the prior art illustrating post-injection needle sheaths. The fluid chamber and the needle are in axial alignment. The device provides an assembly which employs a compression spring between the body of the needle and a protective cap. Prior to the injection, the distal end of the needle is disposed through an opening in the cap, the cap being in frictional engagement with the body holding the spring in a compressed position. After the injection, the cap is released thereby allowing the spring to extend. When the spring is in the extended condition, the distal end of the needle is misaligned with the opening in the cap so that the distal end is prevented from again passing through the opening in the cap.
The problems inherent in this device are representative of those which are exhibited in other devices which have sought to employ post-injection safety sheaths. The devices taught by the prior art contemplate that the spring will be in a compressed condition during use of the needle and until withdrawn from the patient. In substantially all devices disclosed by the prior art, the protective cap must be dislodged manually. Since the caps are generally maintained in place through a frictional fit, the user must employ both hands, one to hold the syringe, the other to release the protective cap. Since the protective sheaths are substantially adjacent the needle tips, the risk of accidental contact with the distal end of the needle is acute.
The present invention substantially resolves the problems inherent in the devices taught by the prior art. A hypodermic syringe constructed in accordance with the present invention employs three parallel chambers, a central chamber and two adjacent slide chambers located adjacent to and on diametrically opposed sides of the central chamber. The hypodermic needle extends from and is coaxially aligned with the central chamber and is coupled to the central chamber by means of a conventional needle hub. This permits the present invention to be employed both for injecting medication into a patient and, with conventional modifications, for withdrawing blood from the patient. A protective sheath is coupled to two needle sheath guides, each being slidably disposed within one of the slide chambers. A helical spring is disposed intermediate each of the needle sheath guides and the axial terminus of the respective slide chamber. When the springs are extended, the attached protective sheath will enclose the distal end of the needle. When the helical springs are compressed, the needle tip will be exposed for its intended use. A release tab extends laterally into each of the needle sheath guides and the wall of the respective slide chamber wall at a location substantially removed from the distal end of the needle. Either during or after withdrawal of the needle, the exertion of manual force on the release tabs will cause the springs in each of the slide chambers to expand thereby forcing the protective sheath about the distal end of the needle.